Rotary hydraulic jack device

ABSTRACT

A rotary hydraulic jack device, intended for controlling a chuck of a machine tool, comprising a rotary hydraulic joint for the alternate placing of each of two compartments of the jack in communication respectively with a source of hydraulic fluid under pressure and with exhaust, each of two fluid-flow paths from the rotary joint to the two compartments of the jack including a nonreturn valve which, for each of the flow paths, is capable of being controlled to the open position by the hydraulic pressure in the other of the flow paths, the fluid-flow path to each of the compartments of the rotary jack being in connection with a pressure accumulator constituted by a cylindrical cavity arranged longitudinally in the rotary tubular shaft of the jack, each cavity containing a compensating piston urged by a spring in opposition to the pressure of the oil.

United States Patent Linux July 1, 1975 1541 ROTARY HYDRAULIC JACK DEVICE 3,213,874 10/1965 Schmiel et al. 91/420 x 1 1 Inventor: Jean Linux, mil-Mamie, 3:22??? 5313?? 5135251611111311111311,,...::1;i:::314258 France [73] Assignee: La Precision Industrielle, Hauts de Primary Examiner-lrwin C. Cohen Seine, France Attorney, Agent, or Firml(arl W. Flocks [22] Filed: Apr. 6, 1973 [21] Appl. No.: 348,598 [57] ABSTRACT A rotary hydraulic jack device, intended for control- 0 ling a chuck of a machine tool, comprising a rotary [30] l Apphcatm Pnorny Dam hydraulic joint for the alternate placing of each of two Apr. ll. I972 Italy 2l/ compartments of the jack in communication respectively with a source of hydraulic fluid under pressure US. Cl. 91/420; 60/ and with exhaust, each of two fluid-flow paths from /60; 279/4 the rotary joint to the two compartments of the jack Cl Flsb 13/042 including a non return valve which, for each of the l l Field Search flow paths, is capable of being controlled to the open 416 position by the hydraulic pressure in the other of the flow paths, the fluid-flow path to each of the compart [56] Refer n s Cit ments of the rotary jack being in connection with a UNlTED STATES PATENTS pressure accumulator constituted by a cylindrical cav- 2,283,961 5/1942 Williamson 92/60 x arranged longitudimlly the nary tubular Shaft 2,359,949 10/1944 Van der Werff 1. 92/60 x of the jack. each a y Containing a Compensating P 2,599,664 6/1952 Sloan 92/106 ton urged by a spring in opposition to the pressure of 2,780,065 2/1957 Spannhake l38/3l X the oil. 2,809,612 lO/l957 Highberg r 92/l06 X 3.145.662 8/1964 Eickmann l38 3l X 2 Clalms 9 Drawlng Figures SHEET 1 ROTARY HYDRAULIC JACK DEVICE This invention relates to a hydraulic rotary safety jack, optionally including a force multiplier, which is intended for controlling a chuck of a machine tool and particularly a chuck of a lathe.

The rotary chucks of hydraulically controlled machine tools are usually provided with rotary control jacks so as to avoid transmitting the force of the jack to the chuck by means of a rotary member which, due to the heavy loading, would wear rapidly.

For supplying such jacks, there is proposed, in US. Pat. No. 2,835,227, which is assigned to the same assignee as the present application, a rotary hydraulic joint having no contact between its solid parts, which enables hydraulic fluid under pressure to be conducted, in a permanent manner, into one or other of the compartments of the jack. The hydraulic fluid is, in general, an oil; it may also be a synthetic fluid which, like oil, has lubricating properties. For the sake of simplicity in this specification, such hydraulic fluid will be referred to as oil.

This earlier proposal has the disadvantage of a certain lack of safety if the chuck is not of the irreversible clamping type; in the event of failure of the hydraulic supply, there is a risk of the chuck unclarnping and freeing the workpiece being machined in a very danger ous manner, owing to the high speeds of rotation used.

it has already been proposed in Swiss Pat. Specification No. 47 L328 to overcome this defect by placing a non-return valve in each of the passageways which, in the rotary part. lead to the two compartments of the jack. To enable evacuation of the oil contained in the compartment opposed to the one which is placed under pressure in the jack, this pressure is employed to force open the non-return valve of the opposed compartment by means of a piston terminating in an axial extension. In addition, between the non-return valves and the jack compartments, there is provided a gas-pressurised hydraulic pressure accumulator which maintains the necessary hydraulic pressure in the jack compartment which has just come under pressure, in the event of leakage of oil in the space placed under pressure which is closed by the corresponding non-return valve.

This last-mentioned embodiment has several disadvantages. Thus, the radially oriented non-return valves which it includes are strongly influenced by the centrifugal force. In addition, this radial disposition associated with the employment of a common central piston for forcing open the two valves in turn by means of the extensions provided at the two ends of the said piston, prevents the provision in the rotary jack of an axial passage which allows the manufacture on a lathe of a series of short articles from a long bar traversing the fixed headstock. The impossibility of providing such an axial passage in the rotary jack has been accepted in said SWiss Specification and, in order to avoid unbalance, the hydraulic pressure accumulator is disposed axially.

The present invention aims to overcome these disadvantages and to provide a jack which is rotatable at high speed and has a normal axial passage therethrough. In addition, the invention not only allows the maintenance of the pressure originally supplied to the jack, but also an increase in the effective pressure which is applied to the jack compartments.

According to the invention a rotary hydraulic jack device comprises a rotary hydraulic joint for the alternate placing of each of two compartments of the jack in communication respectively with a source of oil (as hereinbefore defined) under pressure and with exhaust, each of two oil-flow paths from said rotary joint to the two compartments of the jack including a non-return valve which, for each of said paths is capable of being controlled to the open position by the hydraulic pressure in the other of said paths, the oil-flow path to each of the compartments of the rotary jack being in communication with a pressure accumulator constituted by a cylindrical cavity arranged longitudinally in the rotary tubular shaft of the jack, each cavity containing a compensating piston urged by a spring in opposition to the pressure of the oil.

When the external pressure disappears, the oil accumulated in the cylindrical cavity compensates the possible losses of this oil, whilst the thrust of the spring maintains, in the active compartment of the jack, a pressure which approaches the control pressure the more closely, the less the loss of oil and the less the expansion of the spring.

It is possible to compensate completely this fall of the control pressure, and even to increase, in the active compartment of the jack, the oil pressure with respect to the control pressure, by utilising a differential compensating piston with two displaced sections, the one of small diameter being engaged in the cylindrical space forming the oil reserve, and the other of larger diameter being engaged in a cylindrical space coaxial with the first which, on the side opposed to the small section, contains the said spring and, on the other side, communicates with the control pressure upstream of the non return valve.

Thus, when a compartment of the jack is placed under pressure, the oil acts on the two sections of the piston to ensure the compression of the spring and, when the control pressure disappears, the non-return valve closes communication between the jack compartment and the exterior, whilst the spring compresses the oil in this compartment up to a pressure which is a multiple of the control pressure substantially in the ratio of the area of the large diameter section of the piston to the area of its smaller diameter section.

Under these conditions, if the jack is perfectly oiltight, it can work with a limited control pressure for ensuring the movements and a first clamping. When this operation has been achieved, the operating pressure is reduced to a very low value with the object of permitting lubrication of the bearings of the radial joint transferring the pressure. At this time, however, the pressure which acts in the active compartment under consideration is multiplied in the ratio 8/5 in which 8 and s are, respectively, the larger area and the small area of each differential piston. For example, if 5].: 5, the operating pressure being 20 bars, the pressure developed after the over-pressure effect will be 20 X 5 bars.

It is thus possible to make use of a jack having active surfaces of small size and, as a result, an assembly possessing a reduced angular momentum. which is a valuable property in modern machines in which the high speed spindles lead to reduced machining times and, as a result, frequent starts and stops, which are particularly detrimental to clutches and brakes.

The very low pressure, for example 2 bars, which may be admitted into the jack during the time of use other than the operations of clamping and unclarnping, considerably limits the heating of the assembly and of the oil of the hydraulic generator since, in order to de' velop the same force in the jack, a pressure of 100 bars would have to be continually applied.

The invention will now be described, by way of exam ple, with reference to the accompanying drawings, in which:

FIG. I is a schematic axial section view of a first embodiment of the invention, this Figure showing, for the sake of clarity, the members distributed in two different radial planes. This Figure corresponds substantially to two radial sections inclined to one another at an acute angle and joined according to the line XX,

FIG. 2 is a schematic view ofa more evolved emobdiment of the invention, permitting compensation of possible losses of pressure oil and if necessary the creation of an overpressure,

FIG. 3 is an elevation of the rear of the jack shown schematically in FIG. 2,

FIGS. 4 and 5 are sections taken on the lines IV-IV and V-V respectively, of FIG. 3, the jack parts being shown in different positions in the upper and lower halves of these two Figures,

FIG. 6 is a section taken on the line VIVI of FIG.

FIG. 7 is a section taken on the line VIIVII of FIG. 6, and

FIGS. 8 and 9 are sections taken, respectively, on the lines VIIIVIII and IXIX of FIG. 5.

In the embodiment shown in FIG. 1, the numeral 1 designates the head of a cylinder 2 of a rotary hydraulic jack, the head I being fixed to the hollow spindle (not shown) of a machine tool. The cylinder 2 contains an annular piston 3 formed integrally with a sleeve 4 provided, for example, with a screw-thread 5 for exerting a pull on a control member (not shown) of a workholding chuck (not shown) mounted at the other end of the spindle.

The annular piston 3 is traversed by a tubular rod 6 fixed to the cylinder 2 in a radial plane which bisects the solid acute angle between the two radial planes which together constitute the section shown in FIG. I.

For the practical construction of such a rod 6, and indeed for the construction of other details of the jack illustrated in FIG. I, reference should be made to FIGS. 2 to 9, since the embodiment shown in these latter Figures has numerous points in common with that illustrated in FIG. I.

The piston 3 defines in the cylinder 2 two compartments A and B which can be placed under pressure alternately by means described hereafter, the compartment B receiving oil through the interior of the rod 6.

The cylinder 2 is extended by a cylindrical tubular portion 2a which, by means of bearings 9 and 10, is centred in, and rotates in, a fixed sleeve ll, which is mounted in an internal sleeve 12 forming an integral part of an oil-collecting casing 13.

In the internal wall of the sleeve II are machined two grooves a and b which communicate through radial borings with pipe unions 14A and 148, respectively, for supplying these grooves with oil under pressure or connecting them to exhaust i.e. to a reservoir of oil (not shown) at atmospheric pressure. It will be noted that the union 14B is in a different radial plane from the union 14A and that both of them are situated outside the radial planes of the section illustrated.

As in the case of the previously mentioned U.S. Spec ification No. 2,835,227, all contact is avoided between the parts 11 and 2a, and the oil pressure in the grooves is maintained owing to the large loss of head which is produced by the wire-drawing of the flow of this oil in the annular gap between these two parts in relative rotational movement. The oil which escapes lubricates the bearings 9 and 10. Oil which escapes from the jack compartment A past an O-ring seal 16a between the tubular portion 2a and the sleeve 4 is trapped by a further sealing ring 16b, having a four-lipped section, and is evacuated through a conduit 15. All the escaping oil flows into orifices 17 and thence into the envelope 13, from which it is evacuated through a pipe union 18.

The grooves a and b communicate, respectively, with the jack compartments A and B, as described in U.S. Specification No. 2,835,227.

It is clear that a permanent clamping of the jack can only be obtained with oil supplied permanently to one of the grooves, the other groove being in connection with the return tank through the corresponding pipe union. In order to avoid this disadvantage of having to maintain a high permanent oil pressure, in the embodiment shown the tubular portion 2a includes two borings 20 and 21 which open into the compartment A of the jack. The central narrow part 20a of the boring 20 contains a solid piston 23 which has two pointed extensions 24A and 24B,

Disposed in the boring 20, and facing one another on opposite sides of the piston 23, are two ball valve seatings 25A and 258 containing, respectively, balls 26A and 26B subjected to the action of compression springs 27A and 278. The spring 27A bears against a sleeve 28 which provides a free passage to the compartment A, whilst the spring 278 bears against a plug 28, which is itself maintained in place by an annular cover 30 secured to the end of the portion 20 by screws 31.

The boring 21 contains two pistons 32A and 32B separated by a spring 33. The piston 32A is subjected directly to the pressure reigning in the compartment A. The piston 32B bears against a stop 34 formed integrally with a plug 35 which also bears against the cover 30. The stop member 34, 35 is disposed in an enlarged portion 21a of the boring 2I which, via a boring 36 formed in the wall of the tubular portion 2a, communicates with a part 20b of the boring 20 situated between the plug 29 and the valve seating 258. The longitudinal boring 37, shown in chain lines, which connects with the boring 36, corresponds, as indicated by the arrow 38, with the interior of the tubular rod 6 for evacuating the jack compartment Bv The arrangement of FIG. I functions as follows:

Let it be assumed that the piston 3 is in a midposition in which the compartments A and B are substantially equal, and that it is desired to move the piston towards the right by supplying oil under pressure to the compartment A. With the union 14A, and thus the groove a, under pressure, the oil can force past the valve formed by the ball 26A in order to pass towards the compartment A through the sleeve 28, but since the flow of oil from the compartment B is prevented by the ball 268, the flow of oil into the compartment A is not directly possible.

However, since the pressure is rising in the groove 0. whilst it is zero in the groove b connected to exhaust via the union I43, the piston 23 is displaced towards the left and its extension 248 forces open the ball valve 268, so that oil from the compartment 8 can pass to exhaust via the hollow rod 6 (boring 37) the boring 36.

chamber b, and the groove h. Oil can then enter into the compartment A.

As the pressure in the compartment A rises, the piston 3 moves to the right and starts its clamping action. At the same time the piston 32A is thrust back in opposition to the spring 33, the latter bearing against the piston 32B.

In this situation, it is possible. if desiredgto maintain the clamping pressure in the groove a.

In the event of failure in the hydraulic device and the loss of pressure in the groove 11, the ball valve A, 26A closes under the influence of the spring 27, and a certain pressure is maintained in the compartment A by the thrust of the spring 33 on the piston 32A.

It is also possible to use systematically this hydraulic locking property in order to reduce abruptly the pressure of the oil after clamping and to function under reduced pressure, for example two bars, which is sufficient for the lubrication of the bearings and for cooling without the need for changing the oil.

It is to be noticed that the balls of the valves, as well as the springs which bear on them, are subjected to centrifugal force, which is capable of altering the function. It will be noticed, however, that these balls are in practice situated on the smallest possible radius of the rotating jack, having regard to the existence of the axial passage through the jack. Moreover, the balls may be made from a light metal, for example from oxidised anodic aluminium.

Finally. it will be noticed that the valve seatings 25A, 258, may be engaged simply in the corresponding borings, Under the effect of the pressure. they behave as valves and are not influenced by the movement.

When the groove h and the compartment B are, in turn, placed under pressure, the piston 23 is moved towards the right and the pressure is maintained by the piston 32B bearing, via the spring 33, on the piston 32A which is then stopped against a plug 39. The space between the two pistons 32A, 328 communicates with the exterior through a conduit 40, so that the air trapped between them does not disturb the functioning of the jack.

The embodiment illustrated in FIGS. 2 to 9 has numerous analogies with the embodiment that has just been described and similar members carry the same reference numerals. In this embodiment, however, the non-return valves are of the slide valve type, each valve being movable to open position by an independent piston-operated push rod, Finally, the pistons for maintaining the pressure are arranged to increase this pressure.

The principle of operation is illustrated by FIG. 2.

Between the grooves a and h and the compartments A and B are disposed, respectively, the non-return valves 41A and 41B and, due to the provision of the crossed branch connections 42A and 428, the placing under pressure of one of the two grooves opens the non-return valve associated with the other groove.

The small sections 44A and 44B of two similar differential pistons 45A and 458. each subjected to the thrust of a spring 46, receive, downstream of the nonrcturn valves. the pressure reigning in the corresponding compartment of the jack. In addition, the pressure of the control oil, upstream of the non-return valves, is applied via the by-pass lines 47A and 478 to the annular surfaces 48A and 48B of the differential pistons.

Thus. as before, when the pressure of the oil is applied to one of the grooves, for example groove u, the

.non-return valve corresponding to the other groove is forced open and the differential piston, acting as a hydraulic energy accumulator, is displaced in opposition to its spring 46. During this control. the control pressure acts simultaneously on the small section of the differential piston and on the annular area between the small and large sections, that is to say on the total area of large diameter of this piston, in order to compress one of the springs 46 which thus accumulates a high elastic energy. When the control pressure disappears (accidentally or voluntarily), the thrust of the spring 46 is applied to the small section only of the differential piston in question.

Assuming that, at the time of cutting off the control pressure, the spring 46 does not have its state of compression modified, that is to say it returns entirely the thrust which it has received, the pressure in the compartment of the jack will be multiplied in the ratio 81s in which S and s are the areas, respectively, of the large and small sections of each differential piston.

lnversely, since the springs 46 are strongly compressed, such a device allows, through the possible stroke of the differential piston, a certain loss of oil before the pressure will be lowered to the level of the control pressure. Thus, in one embodiment, for a control pressure of 30 bars, the loss of oil may attain half a cubic centimetre, without falling below this control value, It is still more than a twentieth of a cubic centimetre for a pressure of five bars.

In the practical embodiment illustrated, the differen tial pistons 45A and 45B are housed in shouldered axial borings 50A and 505. As shown in FIGS. 5 and 9, a direct connection of the groove a with the annular chamber defined in the boring 50A by the piston 45A, is obtained by a short radial boring 51 starting from the groove 0 which intersects an oblique boring 52 closed by a plug 53.

Via a boring 55 (FIG. 4), the pressure in the groove 0 acts directly on the head 56 of the valve 41A which, applied against its seat, obturates the communication with the chamber A through a conduit 57. This conduit serves as a support for one end of a spring 58 of the valve, the conduit being retained by a spring ring 59. Moreover, the head of the hollow valve is thinned down and includes radial borings 60 for placing the oil supply in communication with the conduit 57.

Through a radial orifice 61, the groove a is in direct communication with a cylinder 62 containing a piston 63B intended to force open the valve 418. The latter is arranged, like the valve 41A, to place the groove b, via a radial opening 64, in connection with the tubular rod 6 which communicates with the compartment B.

Through a radial boring 65 (FIG. 5), the groove 1) is also in direct communication with the boring 505 in order to act on the annular area of the differential piston 458. Moreover, (see FIGS. 6 and 7), via a boring 66, an axial boring 67 and a transverse boring 68, the groove h is placed in communication with a cylindrical space 69 which contains a piston provided with a pushrod 63A intended to act on the valve 41A.

Through a transverse conduit 70 (FIGS. 4 and 8) which connects the boring 508 with a boring 71 containing the valve 418 and the end of the tubular rod 6, the pressure ofthe compartment B is transmitted to the small section 44A of the piston 45A.

Thus, upstream of its associated non-return valve, each of the grooves a and b is associated with three paths, one towards the said valve, the second towards the piston which forces open the other non-return valve, and the third which terminates at the annular chamber of the differential piston which compensates or amplifies the pressure, the small surface of this piston being in direct communication with the corresponding compartment of the jack.

The invention is applicable to the control of chucks of machine tools and especially of lathes having high speeds of rotation.

What is claimed is:

l. A hydraulic jack device comprising a rotary cylinder,

a piston in said cylinder parting the same into two compartments,

conduit means including rotary joint means for connecting each of said compartments to a source of liquid under pressure, said conduit means including, between said rotary joint means and each compartment, a liquid flow-path provided with a pressure responsive nonreturn valve,

pressure operated piston means for forcibly opening a respective non-return valve in one flow path responsive to pressure in the other flow path,

first duct means connecting said piston means with each flow path upstream of said non-return valves,

associated with each flow-path, means defining a stepped cylindrical cavity comprising a first portion of small diameter and a second portion of large diameter forming an extension of said first portion,

second duct means connecting the end of said first portion remote from said second portion with the associated flow-path downstream of the corresponding said non-return valve,

a differential piston in said cavity having two sections secured to one another and respectively cooperating with both cavity portions,

a spring in said second portion urging said piston to ward said first portion,

third duct means connecting the annular space comprised between the junction of said portions and the two sections of the differential piston with the associated path upstream of the corresponding non-return valve.

2. A hydraulic jack device adapted for equipment of a lathe headstock, according to claim 1, wherein said cylinder with said piston mounted thereon is tubular, an axial tubular extension of said cylinder, said rotary joint means being arranged on said axial tubular exten sion of said cylinder, and wherein, in said tubular extension, said non-return valves and piston means are located in axial bores, and said cavities are axially bored in said tubular extension, and said flow-paths and duct means are drillings also pierced in said tubular extension.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 165 Dat d July 1, 1.9 75

Inventor 5) Jean Lioux It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 11 should read:

Apr. 11, 1972 France 12621/72 Signed and Sealed this thirteenth Day of Aprill976 [SEAL] AIIESI.

RUTH C. MASON C. MARSHALL DANN Ara-sling Officer (mnmissinm-r ufIan'ms and Trademarks 

1. A hydraulic jack device comprising a rotary cylinder, a piston in said cylinder parting the same into two compartments, conduit means including rotary joint means for connecting each of said compartments to a source of liquid under pressure, said conduit means including, between said rotary joint means and each compartment, a liquid flow-path provided with a pressure responsive nonreturn valve, pressure operated piston means for forcibly opening a respective non-return valve in one flow path responsive to pressure in the other flow path, first duct means connecting said piston means with each flow path upstream of said non-return valves, associated with each flow-path, means defining a stepped cylindrical cavity comprising a first portion of small diameter and a second portion of large diameter forming an extension of said first portion, second duct means connecting the end of said first portion remote from said second portion with the associated flow-path downstream of the corresponding said non-return valve, a differential piston in said cavity having two sections secured to one another and respectively cooperating with both cavity portions, a spring in said second portion urging said piston toward said first portion, third duct means connecting the annular space comprised between the junction of said portions and the two sections of the differential piston with the associated path upstream of the corresponding non-return valve.
 2. A hydraulic jack device adapted for equipment of a lathe headstock, according to claim 1, wherein said cylinder with said piston mounted thereon is tubular, an axial tubular extension of said cylinder, said rotary joint means being arranged on said axial tubular extension of said cylinder, and wherein, in said tubular extension, said non-return valves and piston means are located in axial bores, and said cavities are axially bored in said tubular extension, and said flow-paths and duct means are drillings also pierced in said tubular extension. 